The Cal-look Lounge

Anyone run into a problem with Type 1 brakes, that the (German) master cylinders produces residual pressure on the front circuit, but without any residual valves in place? Trying to use front (CSP) disc brakes and I am going batshit trying to get them from dragging... And yes, the pushrod has been shortened....

What kind of brake lines? And how old?

The pistons in the caliper need to be free. in effect the piston seal pulls the piston back a little as the pedal is released. any rubbish, rust etc can stop the piston moving back freely. I'm thinking your car may have sat for a long time and brake fluid is hydroscopic (absorbs water) and there might be a bit of rust in the calipers.

Now, I like the way you think.... This is most interesting... Thanks.

ALL, as in everything is brand new! All stainless hard lines, and stainless "flex" lines used.

If they are both dragging equally the problem has to be with the master and pushrod/pedal setup. If the pistons are hanging up due to rust, likely one side will be different than the other. Try pushing the pistons back into the caliper with a screwdriver and see if they move freely.

Thanks,!

Deano,
Being that you mentioned something I had not heard about doing, how much did you shorten the pushrod to the master?
I'm in the early stages of bleeding up a completely new brake system in my '67 (ACE discs front,Type3 rear) and before I get to far along, maybe I need to make some More changes.
Thanks, Steve

At this point in the process, I have probably shortened the pushrod too much, but until I figure out what is holding pressure, I will keep it this way to insure it is not bottoming out. Stick with the book on this one. I will adjust this pushrod correctly, once I have figured out the overall problem.

Dean, I figured with you being at the lead of that which is new and better, your mention of shorter brake pushrod was a new "Hot Ticket" trick.

Thanks for your reply. 
Steve

What size stainless flex line did you run? To small constricts the flow back to m/c since its not under pressure to return. Something to consider

Upon teardown, both front caliper pistons were either nearly frozen or not moving freely. I had to use a punch through the fluid hole to "push" out the piston. Found a brown haze on cylinder wall... Not good. Lightly sanding the bores now (with 1000# paper), and the pistons move up and down.. Good call on your part! Thanks.

Just for future reference . . . this is a good one to remember also. I replaced the calipers on my Ghia (and tossed into the trash a pair of good calipers!) be for I discovered the flex hoses had swelled closed. The outsides looked PERFECT!!! The master was able to build enough pressure to push the fluid past the obstructions, but the calipers could NOT push the fluid back. It was as I disconnected the hoses to replace the master cylinder that I found them blocked.

All the best with yours Deano . . . let us know how it turns out.

Deano,
How did you check the pistons for free movement? By hand? It might take some force because they are a snug fit in the bore with tight fitting square o-ring seal. By design, the square o-ring is all that returns the pistons to a rest position and this is what keeps the brakes "self adjusted". Could the brown haze have been the remnants of an assembly paste?

Typically you would mount the caliper in a vise and apply air pressure to the open hose port with a rubber tipped blowgun to pop the pistons out. You can also place a block of wood inside the pad area to prevent them popping all the way out and only apply a little pressure to watch them move. I do this after an OH of them to ensure their movement.

Anyway, have you verified on the car that they don't drag anymore? If they still do a simple way to rule out the M/C is to apply the brakes once so they lock up, then loosen the bleeder or hose to release any pressure and see if they free up.

As far as the push-rod free play adjustment, it really shouldn't be shorted too much to obtain the play, the pedal stop is what the service manual say's to adjust. Their fear is that the push-rod will end up being too short overall and in a failure situation the pedal may bottom out against the bulkhead before the push-rod has pushed the M/C piston fully. All you need for free play is about 1mm between the tip of the push-rod and the M/C piston. This works out to about 1/2" play if measured at the top of the pedal pad.

After I took both calipers apart and lightly sanded the what appears to be surface rust and a few pits, I cleaned them, and then assembled. I tried the air nozzle trick and NOW, they both move out quickly and without too much effort (not like before). After all this, if I still see some drag, then, its time to dig into that master cylinder. Thanks for all the tips. Deano

I had this exact issue at bug jam last yr.   Pushed the brakes on and they stayed on.   Gaffes with them for 20mins and they were free.   Thought I'd solved it then moved off.  Pressed the brakes and locked on again.  They free off eventually so all my faffing wasn't what fixed it.  It was just the time.    Completely collapsed inside. 
Tho odd was that to replace them I had to use drum flex lines instead of disk ones because he end of the flex was domed rather than dished.   Weird.  But the disk flex hoses just wouldn't sit in the caliper and seal.   

Just a dumb question, how long has it been since the calipers were bought to the time they were put to use? Would this be a good justification for bleeding brakes on a regular basis?

Brian, I hate to say it but in my case, those calipers and wheel cylinders have been sitting in my office, and elsewhere, for nearly 8 years plus! I learned my lesson about using cast iron brake parts without checking them inside before using them. No telling how long, and where (climate) they have been sitting.

    Deano

 Are you able to drive the car now with no more brake issues.

Frenchy

I wish... Had to rebuild both front calipers, and then I found a bad caliper bracket (stripped out threads), which now has to be replaced, via Germany. Hope to have that part by Friday, then another bleed the brake session, and then hope that this will fix the (problems). It's ticking me off to see this car sit and not be able to cruise it, with these on-going brake problems. But I do think that that one sticking caliper was the biggie....

You can bleed the caliper without a rotor.  Hang the caliper with wire (coathanger?), and tape a block of steel in between the pistons. When the mounting bracket arrives, you will be partly done.
Other solution. Weld up the hole in the bracket, redrill and tap.

Edited for clarity.

Great ideas. I though of the dummy bleed way. I also figured I would TIG those holes up and re-tap them. But the guys at CSP had them in stock and they are on their way. Should be bleeding brakes by Saturday morning.

Might do a Helicoil or a Keensert to your bracket. I use them all the time. Use a mill to insure proper location and a straight install.

Okay gang, here is a think question.... Why do VW master cylinders (am I am sure many others) have two feed lines for the front brakes, while the rears only use one?

Good question... Maybe just because of the location? Easier to just run two short hard lines instead of a short hard line, a "T", and short hard lines leading to the soft lines?

I'm with Zach on that. A short line run to a tee fitting would require more parts . . . multiplied by millions of Beetles = $$$$$

The rear tee fitting is bolted down. A tee on front might need to be attached the same way. So . . . the cost to weld a bracket plus a bolt, washer, nut, brass Tee, and a hard line, OR drill and tap one more hole in the master cylinder.

Another cost factor is the additional time required on the factory assembly line. An additional hard line is two more connections to tighten and where leaks could occur! Again, if we are talking even only a minute . . . multiplied by millions of Beetles . . . 

Okay, would the functionality of the front brakes change, if you only ran one line from the (a) master cylinder?

Could it be a fluid flow issue? Front wheel cylinders are larger than rears.

Zero.....it's hydraulic.   thousands of people do it when they plumb a line lock in.

I think that's just how the braking system is proportioned  . . . front to rear. The larger wheel cylinder exerts more force to the shoes.
If flow were the issue, larger i.d. lines, from the master cyl. to the wheel cyl., would be needed.

As Taylor is saying, it's pressure that counts. Many cars have a master cylinder with only a single line for the front and another line for the rear, each having a tee to go right and left. In some cases that is because of additional componets in the braking system (combination valve or A.B.S. to name two), but again, with VWs I think it is simply the cost thing.

Learned something today... Inside most VW dual master cylinders, there are check valves on both circuits. These are actually a small, thin brass washers fitted under the rubber cups, that act as check valves. If you use disc brakes, you can remove these washers to allow the fluid to flow back into the reservoir easier, and reduce line pressure (great for drums, bad for disc). If you look closely at this aluminum piston assembly, you can see three small holes drilled into the flange, which backs up to these washers. On VWs' drawings, they are called #28; cup washer....